Synchronous ductal carcinoma in situ of the breast and within epithelial inclusions in an ipsilateral sentinel lymph node.

Epithelial inclusions in the axillary lymph nodes are very rare and have even less commonly been reported with either benign or malignant changes. We present a case of synchronous high-grade micropapillary ductal carcinoma in situ arising in the breast and in an epithelial inclusion in an ipsilateral sentinel lymph node. Despite extensive sampling, no focus of invasive carcinoma was identified. This unique case highlights the difficulty in diagnosis of metastatic disease when there is a malignant change in an epithelial inclusion in a sentinel lymph node and highlights the need for very careful histologic assessment of such lesions.